There have conventionally been proposed various laser projectors that use an MEMS (micro electro mechanical systems) mirror or the like as a deflection apparatus to two-dimensionally deflect laser light to two-dimensionally scan a projection surface therewith, to thereby display a two-dimensional image on the projection surface. Such laser projectors employ either a polarization separation method or an angular separation method as a method of separating light incident on the deflection apparatus and light reflected by the deflection apparatus from each other.
The polarization separation method makes use of polarization to separate incident light and reflected light from each other. For example, Patent Literature 1 listed below discloses a projector that employs the polarization separation method. With this projector, laser light (for example, S-polarized light) is reflected by a PBS to be converted to circular polarized light by a ¼ wave plate, and thereafter, the circular polarized light is made to be perpendicularly incident on an MEMS mirror, while reflected light projected perpendicularly from the MEMS mirror is converted to P-polarized light by the ¼ wave plate, and the P-polarized light is transmitted through the PBS to be perpendicularly projected onto a screen.
Such a polarization separation method, in which light from the MEMS mirror is perpendicularly projected onto the screen, is advantageous in that less trapezoidal distortion occurs in an image (projected image) displayed on the screen, but it suffers from the following disadvantage. That is, when the projector is placed on a desk or on a floor when it is in use, the lower half of the projected image is displayed on the desk or on the floor, and thus the projector needs to be held by hand to display (project) the image on the entire screen. Holding the projector by hand is not preferable, since the projector is liable to be shaken, and it is difficult to keep using the projector for a long time. If, to cope with these disadvantages, the projector itself is placed tilted on a desk while it is in use, then trapezoidal distortion occurs due to oblique projection. Also, in order to obtain a color image as a projected image, it is necessary to use light of red (R), green (G), and blue (B), but it is difficult to design the above-mentioned PBS and ¼ wave plate such that a preferable optical characteristic can be obtained with respect to light of each color of red (R), green (G), and blue (B). Thus, loss is liable to occur with respect to light having a wavelength different from a designed wavelength, and this makes it difficult to obtain a bright projected image.
On the other hand, the angular separation method is a method in which incident light and reflected light are separated from each other by making laser light incident on a deflection apparatus from an oblique direction. With the angular separation method, light reflected from the deflection apparatus is projected obliquely with respect to a screen, and thus, even when the projector is placed on a desk, it is possible to display an image over the entire screen. In addition, since optical members such as the above-described PBS and ¼ wave plate are not necessary, the method is free from the above-described disadvantageous loss of light amount. Therefore, it can be said that the angular separation method is superior to the polarization separation method in terms of usability of a projector and brightness of a projected image.